The cystic fibrosis transmembrane regulator (CFTR) is a CI channel. In cystic fibrosis (CF), CI transport is reduced because the CFTR is mis-trafficked, or has different maturation, stability, or unit conductance. Regulation of the function of other ion channels is also aberrant in CF, and airway cells have increased inflammation and bacterial infection. The long-term goal of this proposal is to reduce the severity of cystic fibrosis by activation of another chloride channel, CIC2. CIC2 CI channels are found in the same airway epithelia as CFTR, and activators of CIC2 that function in vivo, have been identified. CIC2 mRNA has not been shown to be up-regulated in CF. However, in collaborative studies, the mRNA for the Kir4.2 K channel was found to be up-regulated in the lung of several murine models of CF using genomic approaches. The cloned and expressed channel is PKA-activated. This K channel may help promote CI transport by residual F508CFTR and other CI channels including CIC2. The key questions to be addressed in this proposal are whether activation of CI transport by activation of CIC2 directly (or indirectly through activation of this K channel) will be sufficient to compensate for loss of other functions observed in CF. The Specific Aims are to: 1) Establish whether CIC2 function can be separated from CFTR function by using pharmacological and molecular biological approaches; 2) Define the role of CIC2 in airway cell models cultured in conditions similar to the airway microenvironment by using pharmacological and molecular biological approaches. 3) Define whether correction of the CI transport defect by CIC2 activation affects other CF-related changes in function. Na transport (ENaC) function, Ca-activated CI channel (CLCA2) function, and markers of inflammation and bacterial susceptibility will be studied; and 4) Define the role of up-regulation and activation of Kir4.2 K channel in CF. This will also be studied in terms of CI transport, Na transport, CLCA2 function, inflammation and bacterial susceptibility.